Provided is a pressure sensor, which comprises a housing with a pressure port projecting into the housing and which is equipped with a micro-mechanical pressure sensing element that is arranged in the housing. The pressure sensing element is connected to the pressure port in such a manner that it seals a passage of the pressure port, by way of which a pressure acts directly on the pressure sensing element. In addition, a method for manufacturing such a pressure sensor is provided.
Such pressure sensors are used for monitoring the pressure or the pressure fluctuations in various fields of applications exhibiting widely varying pressure ranges. For example, in control units for piston motors or in piston compressors the requirements with respect to the pressure stability, the temperature range and the service life are very stringent. In particular, under very high and to some extent sudden pressure fluctuations and the maximum pressures, which may occur there, the reliability of the pressure loaded connections, which are often designed as cemented joints, must be guaranteed under all operating conditions.
A typical design of a pressure sensor is described, for example, in U.S. Pat. No. 7,024,937 B2. A pressure-sensing element is mounted with its diaphragm over the passage of a pressure port, so that a pressure, which is applied in the passage of the pressure port and is supposed to be measured, acts on the diaphragm. The opposite side of the diaphragm, which is often called (as also below) the front side of the pressure-sensing element, has measurement resistors, by means of which the change in the resistance of the applied pressure or a fluctuation in the pressure is supposed to be determined. The resistance fluctuation results, as known in the prior art, from a deflection of the diaphragm from its quiescent position as a consequence of a change in the applied pressure and the associated tensile load or pressure load on the diaphragm. The pressure sensing element and the pressure port, including the necessary electronics, are mounted in a housing in that the pressure port is adhesively cemented to the housing. A comparable pressure sensor is also described in DE 102 60 105 A1. However, the description in that document does not relate to a surrounding housing.
When pressure is applied, the connection of the pressure-sensing element on the pressure port and similarly also the connections between the pressure port and the housing are under high tension. This tension leads, especially at high pressure and long-term usage of the pressure sensor, to reliability problems. The reliability problems are aggravated by bubbles or channels or the like in the cemented joints, all of which impair the pressure tightness and can cause the connection to detach at least in some places.
These problems increase with the statutory requirement stipulating the use of lead-free materials, since it is possible only with difficulty to produce with respect to the pressure and the temperature reliable cemented joints between the lead-free components of a pressure sensor, as described, for example, in EP 1 785 710 A2, or to produce reliable cemented joints, which are made of other materials that are capable of withstanding higher chemical and mechanical stresses, over the entire field of application.
Therefore, the object of the invention is to provide a pressure sensor that exhibits tight and durable cemented joints even at high pressures and pressure differentials while simultaneously using lead-free materials.